A common propulsion drive for work vehicles such as skid steers is a hydrostatic drive system. Hydrostatic drives are advantageous because they are capable of providing a range of different speeds without the need for mechanical gearing assemblies. Hydrostatic drives are based on a hydraulic pump or pumps which are powered by the engine of the work vehicle. The engine is a conventional diesel or gasoline engine having a flywheel which turns the pump. Thus, the pump speed and corresponding fluid flow rate is directly proportional to the engine speed.
The hydraulic pump has a displacement chamber for hydraulic fluid. The fluid flow is controlled by a swash plate which controls the length of the displacement chamber. The length of the displacement chamber moderates the hydraulic fluid flow produced by the pump. The pump is fluidly connected to hydraulic devices such as hydraulic cylinders for driving various actuators, such as lift arms or ground stabilizers, attached to the work vehicle. The hydraulic pump is also fluidly connected to a drive motor. The fluid flow from the pump causes the drive motor to rotate the axles which drive the wheels and in turn the work vehicle. Typically, the right and left wheels of a work vehicle have separate motors.
Present hydrostatic drive trains are susceptible to stalling the engine by placing too much strain on the hydraulic pump due to an increase in power demand. When too much hydraulic fluid flow is required for driving the vehicle or operate hydraulic actuators, the engine may stall, thus cutting off all hydraulic fluid flow from the pumps. Additionally, there may be circumstances where it is desirable to supply additional hydraulic fluid flow to one of the side motors. This may occur in the case of an imbalanced load or travel on a slanted surface.
Such differences in power to the right and left side motors must be addressed manually by the work vehicle operator. Such an adjustment is difficult for an operator to maintain. Additionally, when an operator fails to properly control fluid flow, the engine may stall out. Finally, although hydrostatic drive trains provide precise turning control, often an operator cannot take advantage of this feature since manual precision operation of both motors is difficult to maintain.
Thus, there exists a need for an electronic hydrostatic drivetrain controller which prevents an engine from stalling. Further, there is a need for an electronic hydrostatic drive controller which provides automatic compensation for additional loads placed on different hydrostatic motors. Finally, there is a need for a hydrostatic drive controller which provides precise control of power from either drive motor in a work vehicle.